The present invention relates to a swirl generator that centrifugally isolates dust particles from air to be fed to an engine and draws the air free from the dust particles to an air cleaner body.
As shown in FIG. 9, this type of air cleaner mainly includes an inlet duct 85, a pre-cleaner 81, and an air cleaner body 86. A swirl generator 80 is located in the pre-cleaner 81. The swirl generator 80 applies swirl force to air 84 that has been introduced into the inlet duct 85. The air 84 thus forms a swirl flow 82. In this state, dust particles contained in the air 84 receive centrifugal force and thus move from the center of the pre-cleaner 81 toward an inner wall of the duct 71. The air 84 thus flows from the left-hand side to the right-hand side as viewed in FIG. 9 and is then sent to the engine. After having reached the vicinity of the inner wall of the duct 71, the dust particles in the air 84 are collected by a dust discharge valve 83, which is located below the duct 71, and then discharged to the exterior of the duct 71. A filter element 88 is arranged in the air cleaner body 86. The filter element 88 removes smaller-sized dust particles from the air 84. In this manner, clean air 89 is supplied to the engine.
For example, Japanese Laid-Open Patent Publication No. 63-192951 discloses a pre-cleaner having a swirl generator. As shown in FIG. 10A, the swirl generator 80 described in this document includes a central portion having a nose cone 91, an outer circumferential portion having a cylindrical ring 92, and a plurality of guide vanes 90, which are provided between the central portion and the outer circumferential portion. The guide vanes 90 are spaced at equal intervals. As shown in FIGS. 10B and 10C, a guide fin 95 is located in an upstream portion of each of the guide vanes 90. A deflecting fin 93 is arranged in a downstream portion of each guide vane 90. Each of the deflecting fins 93 is inclined at a predetermined angle with respect to the corresponding one of the guide fins 95. Each guide fin 95 adjusts the flow of the air 84. The corresponding deflecting fin 93 then changes the flow direction of the air 84. As a result, the swirl flow 82 is formed by the air 84.
The output performance of an engine of a vehicle has been significantly improved in recent years. The engine thus requires a correspondingly increased air supply. However, the size of the vehicle is substantially unchanged before and after such improvement and the engine compartment has only limited space for accommodating devices of an intake system. Yet, a greater number of auxiliary devices must be received in the engine compartment. Thus, to ensure a higher output of the engine, the inner diameters of the intake ducts may be equalized to raise the flow rate of the air sent to the engine. If the swirl generator 80, which is a conventional type, is used to remove dust particles from the air that flows at a higher flow rate, the flow of the air may be separated from the joint portions between the guide fins 95 and the corresponding deflecting fins 93. This not only generates noise in an intake pipe but also disadvantageously influences an engine control system. Specifically, separation of the air flow from the joint portions causes erroneous operation of an air flowmeter, which detects an intake air amount, or loss of the output of the engine due to decreased air intake efficiency. Also, the separation of the air flow hampers the generation of a swirl flow. Dust isolating performance of the swirl generator 80 is thus lowered.
To suppress such separation of the air flow, the angle between each guide fin 95 and the corresponding deflecting fin 93 may be decreased. However, this decreases swirl forming performance of the deflecting fins 93.